Hardware Production
Section 4.4.1.
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Standard Parts and Interfaces to Reduce Cost

In parts and interface standards, we'll be even more narrowly focused than MIL-SPEC. It might seem incongruous, but the trick to successful maintenance programs and lowering spacecraft costs is to legislate the fiddly bits before you even start preliminary design.

Here's an example from the International Space Station program: All bolts that will be operated by the EVA crew are 7/16" double-height rounded hex heads. All of 'em; no exceptions; well, except for the bolts on the CMG's, which I believe are still 3/4" hex heads due to the high torque required to keep the gyroscopes firmly attached to the space station structure.

The bad news is that the EVA spec doesn't tell what the threads must be, just the bolt head. So although you can operate all bolts with the same tools, you can't swap bolts.

For the Artemis Project spacecraft, we'll specify a very small set of allowable shank sizes and thread configurations.

Aerospace companies restore order from the chaos by having their own narrowly defined in-house specifications for fasteners, extrusions, sheet metal alloys and thicknesses, window openings, seat tracks, and parts vendors. Designers are allowed to introduce other stuff into the standard specs, but it's an uphill battle that one begins only if there is a very compelling reason not to use the standard parts. This leads to a little bit of inefficiency in the engineering design, but the loss of performance for carrying around a few extra pounds of metal is more than made up for by the reduction in operating cost.

In these days of Computer Aided Design systems, it's even easier to enforce the rules: A new designer is working on something, and needs a bolt or a screw. He goes into the standard parts library, and -- voila! -- what you see all you got, kid. You must choose wisely.

Besides reducing the need for spares inventory, this lowers cost because every one of those bolts is a known item. We know its structural characteristics, how much variation we can expect from each vendor, and who those vendors are. We know that if we buy MIL-SPEC-GLOBBUS fracture-critical sprockets from Spacely Sprockets, we don't have to test them because we have a long history of experience with the quality of Spacely's products; so we can save a lot of laboratory time by trusting our vendor.

Hardware Production

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